The production of powder-form or granular detergents and cleaners on an industrial scale by the hot spray-drying process starts out from aqueous suspensions or slurries which contain a large part of or even all the detergent ingredients. For economic reasons, it is important that the slurry should contain as many of the detergent ingredients as possible, i.e. should be substantially free from liquid ballast. Accordingly, as little water as possible is used in making up the slurries. However, the degree of concentration is limited by the highest possible viscosity at which the slurry can still just be processed. An important ingredient of most detergents and cleaners are anionic surfactants which are generally used as paste-like concentrates in the form of their alkali or ammonium salts in the production of the detergent slurry. In the case of .alpha.-sulfotallow fatty acid methyl ester for example, the surfactant content of commercial concentrates amounts to around 30% by weight. Pastes having a higher surfactant content cannot be processed.
One feature of the rheological behavior of surfactant concentrates is that they react to the addition of water not by a reduction in viscosity, but rather by an initial increase in viscosity to a gel-like state, giving rise to further problems for the processor. For example, gel lumps that have formed are often not easy to redissolve or, alternatively, valves of pumps and vessels become blocked.
Various proposals have been made with a view to solving these problems. German Application No. 22 51 405 for example describes the salts of certain carboxylic acids, particularly hydroxy carboxylic acids, as viscosity regulators. According to German Application No. 23 05 554, sulfonated aromatic compounds are suitable for this purpose. German Application No. 23 26 006 discloses sulfates or sulfonates of aliphatic, optionally substituted hydrocarbons as viscosity regulators. Publications also disclose the addition of lower alkanols as a possible method of reducing viscosity. The addition of the well-known hydrotropes, such as cumene sulfonate for example, or of acidic phosphoric acid esters (German Application No. 16 17 160) or of polyhydric alcohols, certain carboxylic acids and/or esters of these compounds (German Application No. 8 060) has also been described. It is known from European Application No. 24 711 that the rheological behavior of anionic surfactant concentrates can be improved by adding sulfates of certain polyalkyl ether glycols. It is known from German Patent No. 14 18 887 that an excess of SO.sub.3 remaining in the crude sulfonic acid after the sulfonation of fatty acids or their esters can be removed by reacting the excess SO.sub.3 with stoichiometric or greater than stoichiometric quantities of compounds that react readily with SO.sub.3 to form capillary-active substances, including aliphatic alcohols and adducts of ethylene oxide and/or propylene oxide with aliphatic alcohols. However, there is no indication in this Patent Specification of how to reduce the viscosity of the surfactant concentrate with a sulfonation product containing very little, if any, SO.sub.3.
Some of the additives mentioned in the literature do not work in every surfactant concentrate, some have to be used in high concentrations while others, such as lower alkanols, reduce the flash point of the concentrates.